Actuatable occupant restraint systems, such as air bags and seat belt pretensioners, are well known in the art. Such restraint systems include one or more collision sensing devices, such as for sensing vehicle crash acceleration (e.g., vehicle deceleration). An air bag restraint system further includes an electrically actuatable igniter, referred to as a squib. When the collision sensing device senses a deployment crash event, an electrical current of sufficient magnitude and duration is passed through the squib to ignite the squib. When ignited, the squib initiates the flow of inflation fluid into an air bag from a source of inflation fluid, as is known in the art.
Occupant protection systems utilize a variety of crash sensing devices, which may be either mechanical or electrical in nature. For example, some occupant protection systems include one or more accelerometers that sense vehicle crash acceleration and provides a signal indicative thereof. Systems having an accelerometer further include additional circuitry (e.g., a controller) for monitoring the output of the accelerometer. The accelerometer is operatively connected to the controller, which may be a microcomputer, that discriminates between a deployment and a non-deployment crash event by applying a predetermined crash algorithm to the acceleration signal. When a deployment crash event is determined to be occurring, the controller actuates the restraint.
Air bag restraint systems also are known to require more than one sensor for detection of a deployment crash event. Often, the plural sensors are arranged in a voting scheme in which all the sensors must “agree” that a deployment crash event is occurring before restraint actuation is initiated. In certain known arrangements having plural sensors, the second sensor is referred to as a “safing sensor.” Air bag actuation occurs only if the first sensor and the safing sensor both indicate that a deployment crash event is occurring. Typically, a safing sensor is a directional inertia responsive switch or accelerometer. Consequently, separate safing sensors are required for each crash sensor, which increases the cost of a restraint system proportional to the number of safing sensors being used.